Air batteries generally utilize air as a cathode reactant and have an anode that is composed of a material providing a potential difference from the air cathode, for example Li, Li alloy or Li-intercalated carbon, and a hydrogen storage alloy that has absorbed hydrogen. Other possible anodes are metals that give divalent ions such as Zn, Mg and Ca, those giving trivalent ions such as Al, and alloys of these metals.
With atmospheric air as the cathode reactant, the air batteries achieve a very high energy density. Thus, they are very attractive as next-generation batteries and metal fuel cells.
During discharge, the metal ions flow from the anode and react with the cathode air (oxygen), forming the metal oxide. In the recharging, the metal oxide is reduced to the metal ions and air.
Appropriate catalysts are necessary in order that the oxygen reduction takes place efficiently during the discharge and that oxygen is produced efficiently from the metal oxide during the recharging. Current catalysts used for this purpose include electrolytic manganese dioxide, porphyrin complexes, polymeric cobalt phthalocyanine and platinum as described in Non-Patent Literature 1. However, as mentioned in Non-Patent Literature 2, electrolytic manganese dioxide and porphyrin complexes are labile to oxidation, and the platinum group metals are soluble in solvents, although very slowly, and the dissolved species precipitate on the anode and can induce a side reaction.
Further, various metal compounds are disclosed as air battery catalysts in JP-A-H02-257577, JP-A-2003-200051, JP-A-2004-076084, JP-A-2008-112724, JP-A-2008-270166 and JP-A-2008-300273.